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JEE Advanced levelSingle correct optionDifficulty 3 of 3g2047

A solution in diethyl ether contains benzoic acid, phenol and naphthalene. It is first shaken with aqueous , the ether layer is separated and then shaken with aqueous NaOH. Which row correctly gives the solute(s) found in the aqueous extract / aqueous NaOH extract / final ether layer?

  1. Abenzoic acid / phenol / naphthalene
  2. Bnone / benzoic acid and phenol / naphthalene
  3. Cbenzoic acid and phenol / none / naphthalene
  4. Dphenol / benzoic acid / naphthalene

Answer: A

Hydrogencarbonate is the conjugate base of carbonic acid (pKa1 6.4), so it deprotonates benzoic acid (4.20) but not phenol (10.0). Aqueous NaOH (pH about 13-14) then converts phenol into sodium phenoxide, which goes into water. Naphthalene is neutral and stays in the ether.
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